IN HIS MARVELOUS MEMOIR, Flights of Passage, my friend and onetime colleague Samuel Hynes, a Marine Corps combat aviator in World War II, writes that the war is the shared secret of his generation—those young men who came of age between December 7, 1941, and September 2, 1945. For those of the approximately 12 million Americans in uniform for some or all of those years, it was an experience both personal and collective like nothing before or after. Those who went through the hell of combat carry physical and emotional scars as reminders. But those of us—actually the great majority—who served in the infinite variety of supporting roles also stored up memories that will only die with us.

My duties were in the Signal Intelligence Service, the acorn out of which grew today's mighty oak, the National Security Agency. I translated Japanese radio messages snatched from the ether by our intercept operators and, when possible, decoded by our cryptanalysts. The English renderings by the likes of me were sent on to our war planners. My training, like that of the rest of us overnight Japanese linguists, was hasty and inadequate for any genuine grasp of the language, but it still served to collect vital intelligence.

I'm glad to have had my infinitely tiny part in winning the war, though I still wince a bit at sharing the standing of "veteran" with those who actually risked their lives. But all of us temporary citizen-soldiers understood that we had suddenly been entrusted with the gravest kind of responsibilities, on which many lives could depend. That's the "secret" shared by our shrinking community of now truly old-timers—we grew up together under extraordinary pressures. So do all veterans, of course, but we swarming millions were distinctive in feeling the total outreach, the all-encompassing nature of the worldwide cataclysm that left no one untouched. We were actors in the biggest drama of our century, perhaps of all time.

FOR ME IT BEGAN in the classrooms of New York City's Columbia College, where I was a member of the junior class when Pearl Harbor so rudely interrupted our education. The sudden plunge into hostilities had caught the nation with a critical shortage of Japanese translators. At the time, few Americans studied any Asian languages. The world was still European-dominated, the language of diplomacy was French, and that of international business usually English. Only a few major universities—Columbia among them—offered Japanese instruction, primarily for tiny numbers of graduate students in Asian history, literature, and art. The answer clearly had to be a crash program, like so many others of that feverish spring, to begin teaching the tongue to thousands more Americans, as quickly as possible. I enrolled with a number of good language students in an intensive beginning Japanese class.

Spring flew by in the shadow of almost daily depressing headlines about Allied setbacks everywhere, while I and my Japanese-challenged classmates struggled to memorize the ideographs—little "pictures," each a word—in which so much of the language is written. That summer I undertook eight more weeks of concentrated study at Columbia, six or seven hours a day of classroom instruction five days a week, not including many more hours of homework. We were getting more confident by then, and recruiters started showing up, including one from the Signal Intelligence Service, about which I knew as little as most of America did, reflecting a military policy designed not to draw attention to their work.

The signal corps major wooed us one by one in a midtown Manhattan hotel room. The word "intelligence" never surfaced as he and I played a curious and comical game: I asked him what I would do in the signal corps, and he replied that it would be work of great importance to the war, requiring knowledge of Japanese. And where would I serve? In places determined by the government to have great importance, requiring personnel who used the Japanese language. And that was all that I got. Naturally I took it for granted that we weren't learning Japanese for any purpose other than gathering information about the enemy. I naively believed that I would be translating and interpreting at or near the front, interviewing recently captured prisoners, or quickly translating retrieved documents. I did not realize how ludicrous it would have been for me to fire questions at an exhausted Japanese infantryman who spoke in a regional dialect—or to make out the scribbled handwriting in letters or notebooks carried in uniform pockets. The Army's Military Intelligence Language School in Minnesota mainly put highly trained Nisei to do these difficult wartime interrogations. With rare exceptions: those studying the language only after Pearl Harbor ended up at major collection centers translating documents of long- range strategic value.

I gave the major my okay, in due course ending up at a reception center at Fort Lee in Petersburg, Virginia, for the initiation rites of all young recruits. Within a week, however, we were whisked away to become privates, enlisted personnel of the Second Signal Service Battalion, located at Arlington Hall just outside of Washington, D.C. We lived in hastily built wooden barracks on the sylvan 100- acre campus of a former girls' private school. In the midst of construction to keep up with the battalion's rapidly swelling ranks, we learned about our futures as translators of radio intercepts decrypted in those new buildings whose lights burned all day and night.

Our training was radically different from that at the university. Japanese characters could not be transmitted in the dit-dahs of Morse code. The words had to be vocalized and written out in the Roman alphabet (known as romaji in Japanese). No longer did we have to memorize characters, the hardest part of tackling languages written in ideographs. Besides that, terse military messages in any language require only a fairly limited, if specialized, vocabulary.

I quickly learned to my surprise that I had joined one of the most secret and vital programs of the war. Our specialized studies began under Professor Edwin 0. Reischauer of Harvard, author of the textbook we had used at Columbia and the government's guiding light in accelerated Japanese instruction. He would become the postwar ambassador to Japan, navigating a tricky path toward a new relationship with that country. Reischauer and a pair of associates put us through our daily paces, drilling us in listening to Japanese and translating sample messages.

While the ABCs of cryptology (the making and solving of "secret writing") are simple enough, the practice is wickedly complex. A code is any "language" known only to the sender and recipient of a message, and codes have been used by diplomats, generals, merchants, and clandestine lovers since ancient times. All the two parties need to know is what certain terms signify. For instance, "need cookies" could mean "meet me tonight in front of the bakery," or "send more cavalry." But code- books are necessarily limited in scope. A cipher, on the other hand, substitutes for each letter of "plain text" a different letter, symbol, or number drawn from some "key" table shared with the recipient. That opens an entire dictionary to the creator of a cipher. Without the key the enciphered text resembles gibberish, especially when written without the usual breaks between words but in arbitrary groups.

Any cipher is vulnerable to solution because all languages—or at least all those used by World War II combatants—have certain words, letters, and combinations of letters that are used more frequently than others. (Think of "the" in English.) By isolating these common words and cracking their meaning often by painstaking trial and error, the cipher breaker can use these clues to recover more letters. (Edgar Allan Poe provided an excellent cipher primer in "The Gold-Bug.")

The code maker's job is to disguise these repetitions as much as possible by many layers of enciphering—for example, substituting numbers for letters and then adding yet other numbers to those. But ultimately those buried patterns will resurface somehow, and any cipher can be broken by someone with enough accumulated traffic to work on. IBM machines in the operations building spit out countless punch cards, which sorted thousands of intercepted messages into every conceivable combination of their words and letters. Our job as translators was twofold: to help the cryptanalysts by scrutinizing strings of letters that they brought us in search of Japanese words, and to translate messages already solved. My first assignment was dazzling. One morning I was a student, and the next I was reading a less-than-48-hour-old report from the Japanese ambassador in Berlin to his Tokyo superiors.

My work hinged on one of grandest achievements of the American war effort, the cracking of Japan's major diplomatic code, a machine-generated cipher known as Purple. Like Germany's Enigma machine or our own Sigaba, Purple relied on electromechanical impulses transmitted through changeable arrays of rotors and switches to activate the keyboards of printers that encoded and decoded messages. While such a system vastly speeded up the output of code clerks in the message centers, it also multiplied the possibilities for disguising plain text and tremendously complicated the task of the code breaker. The scientific genius behind the breakthrough, recognized as one of the American fathers of 20th-century cryptanalysis, was Russian-born William Friedman, who worked with mathematicians Frank Rowlett, the principal inventor of the Sigaba, and Solomon Kull- back. By the end of 1940, the trio had cracked the Japanese code and oversaw the building of a replica of the Purple machine in the tiny, secluded offices of the pre-Pearl Harbor Signal Intelligence Service.

The three of them, present at the creation of today's globe-blanketing electronic surveillance system, had become high-ranking officers at Arlington Hall during my stay there, though I don't believe I ever saw them in person. It was a little like working in a telephone and telegraph exchange while Alexander Graham Bell and Samuel F. B. Morse were still hammering out improvements in office suites upstairs.

In January 1943 I saw my first long, partly translated Purple message, which contained Ambassador Hiroshi Oshima's summary of Hitler's intentions in the spring of 1943 from information elicited from Nazi officials. I could not believe that a skinny 20-year-old kid from Queens was translating material that would become part of a top-secret daily summary of signal intelligence findings labeled "Magic," to be read the next morning by President Roosevelt and General Marshall!

It was a thrill that of course could not be shared. The demands for absolute secrecy were obsessive, justified, and sobering. Any breach of security that tipped off the Japanese that their code was compromised would have caused an immediate change, nullified years of effort, and cost lives. Like my companions still wet behind the ears, I was suddenly loaded with a host of frightening adult responsibilities.

Convinced that their encryption was immune to compromise, the Japanese continued to use it throughout the war, giving us a critical window into their high councils. Coupled with our Navy's success in breaking the systems used by the Japanese fleet, our work with Purple provided us with a powerful push toward victory and guaranteed a well-funded future for signal intelligence.

I was only involved with Purple for a short time and was then moved to a quieter front, working on "back traffic" in a shipping code that had expired. It was still useful for accumulating strategic data on Japan's logistical problems and also for identifying sea routes that became hunting grounds for our submarines, but I wanted to get a little closer to an actual scene of war. I managed to finagle a posting to New Delhi in the China-Burma-India (CBI) theater in August 1943.

By the time another translator and I reached New Delhi, after a long and slow passage over the Pacific, another six months had passed. Hardly had we unpacked our barracks bags than news arrived that our soldiers had captured a main Japanese army code- book. The timing was perfect in the CBI. The Japanese had launched an invasion of India, hoping to trigger a widespread revolt against the already expiring British rule. At the same time, a joint British, American, and Chinese task force began a campaign to retake northern Burma from its Japanese conquerors. Behind their advancing front followed thousands of U.S. Engineer Corps troops. They built a remarkable highway known then as the Ledo Road, which twisted over unmapped mountains, across monsoon-swollen rivers, and through dense jungle, providing a critical land connection between India and China.

The first ripe fruit of the code- hook's capture appeared in early March 1944 in the form of a midnight announcement from the Japanese high command in Burma that their 15th Division had started across the Chindwin River along the border between India and Burma. Someone rushed the information over to British headquarters. From then on, most traffic relating to the invasion was diverted to the British cryptanalytic offices, but a flood of information from Burma came our way.

The messages came as fast as our own decoders could process them, and occasionally too fast for the Japanese code clerks themselves. We knew this because we'd sometimes intercept a "service message," or request that a sender repeat a garbled "key." Only my buddy and fellow translator Guy Henle and I were there as translators, because Arlington Hall had anticipated a far more limited CBI operation. For a couple of weeks the two of us worked more or less around the clock, pulling both day and evening duty. We alternated evening shifts so we could grab a little sleep. A third translator, our former classmate Frank Tenny, was rushed out to us by air, and eventually others followed. But for a brief spell in the fierce humidity of the New Delhi spring and summer of 1944, I was absorbed completely and happily in important work. Amid the routine administrative messages devoted to changes of assignment or reorganizations of command structures, there were reports of troop strength and movement. The latter were hurried across the street to G-2 (intelligence) and relayed to Gen. "Vinegar Joe" Stilwell, commander of the frontline units. After a visit to headquarters, our section chief came in beaming one morning to announce that the top brass had ordered us all to "keep it coming."

One night Guy and I spotted a message that kept repeating the non- Japanese word "gu-ra-i-da." We quickly figured out that it meant "glider," the Japanese substituting "r" in place of "1," which doesn't exist in their language. As we translated more of the message, we started to tingle with excitement: it delineated exactly where a small armada of troop- and equipment-carrying gliders had landed inside Japanese-controlled territory—and specified how they were initiating defensive responses. The message also spelled out the name of the American commander of the operation as "fu-ri-pu ka-ku-ran." Both of us repeated fu-ri-pu quickly aloud and came up with "Flip."

"My God," I yelled. "Flip? Flip Corkin!" That was a character in Terry and the Pirates , a favorite comic strip of mine. Corkin was a wise cracking, savvy, and heroic fighter pilot, modeled on Philip Cochrane, a real-life friend and college classmate of the strip's author, Milton Caniff. By 1944 Cochrane—"ka¬ku-ran"—had become a colonel in the Army Air Forces. So the message was the hottest of hot stuff—the Japanese had enough information to prepare a counterstrike against an ongoing airborne operation; because their intelligence had gotten hold of the name of its commander, they might have even more damaging knowledge. We hustled over to the night duty officer, who woke up our section chief He immediately took the translated message to the upper echelons of command.

Our small unit had picked up the first Japanese reaction to Operation Broadway, one of the war's most daring undertakings, in which the Allies built a base far behind Japanese lines in Burma. Gliders towed by paratroop-carrying transport planes had landed engineers, earth-moving equipment, and covering infantrymen in a tiny cleared zone in the jungle. They laid down an airstrip large enough to supply and defend a base of support For British guerrilla units. Known as "Chindits," these special forces inflicted enough damage on Japanese transport and communications to fatally sap enemy fighting strength in Burma.

After that night and those first hectic weeks, work in New Delhi settled into a more or less normal pattern, and everything had a feel of anticlimax. If we were no longer stimulated by the daily grind, there was always the adventure of India itself to combat "desk fatigue." India was overwhelming: the ancient forts and temples, the unfamiliar architecture and decorations, the pungent smells from restaurant kitchens, the variety of incomprehensible languages. I saw in Calcutta the most shattering poverty I have ever witnessed—families conducting their entire lives in the streets, sometimes without even the wretched shelter of a few square yards of cloth stretched over sticks. Sixty-five years ago, extended travel was technologically and financially possible for only a few who traveled by ship. Yet here was the war picking us up and dumping us by the thousands and hundreds of thousands in exactly such places, to gawk and be gawked at. As much as anything, this mighty, swift, and temporary scattering of Americans around the globe— which we were the first to experience on such a scale—linked our own youth to the birth of the current era in which, like it or not, we all truly live in one world.

The scene changed again for me at the end of November 1944 when I was dispatched to Kunming to join

the small signal intelligence detachment in the rear echelon headquarters of the China theater—severed from CBI in a high-level political realignment. Once again I set to translating accumulated backlogs of shipping traffic. The work was not trivial, being of considerable use to our China-based bombers, who continued the methodical destruction of Japan's merchant marine, or at least those parts of it plying China's coast and logistically supporting Japan's huge occupying army. But it definitely lacked the zing of reading daily bulletins minutes removed from Japanese headquarters in Burma.

The war continued to run its course. From halfway around the world we followed the bulletins describing the final dissolution of the Third Reich and cheered the arrival of V-E Day, but we did not anticipate much if any change in our own near futures. It would take a long time to move the millions deployed in Europe to our side of the world and mount the invasion of the Home Islands. The swift end to the war in slightly less than four months after Germany's surrender came as a dazzling and, of course, welcome surprise. I cannot say that any of us expressed a single qualm about the use of two atomic bombs On crowded cities, though the ghastly extent of that destruction and loss of life wasn't fully known yet. I'm now a nuclear abolitionist, but I was not so on that August night, which happened to be the eve of my 23rd birthday, when the Armed Forces Radio announced to us that Emperor Hirohito had agreed to terms of surrender. Pandemonium broke out on the post, bottles squirreled away for just such a moment were produced, work stopped, and a jubilant and very drunken evening followed, with no regrets or reprimands. After a couple of toasts I chose to sit up all night in relatively solemn thought, guarding the classified documents in our office in company with one of the enlisted men.

In mid-December 1945 I steamed under the Golden Gate Bridge, choking up to see the message WELCOME HOME. WELL DONE! painted in white on rocks in the harbor. Then a transcontinental train trip, a reunion with my family before New Year's Day, and finally orders to report to the separation center at Fort Dix. There, while going through the routines of discharge with thousands of others from this vast, various nation, I was once more struck by the magnitude, the sheer vastness of the process that had collected us all from every corner of the United States, scattered us over so many known and little-known parts of the great globe itself, and was now methodically sorting us out and returning us, in many cases unrecognizable to our former selves, from whence we came.

World War II came as close as a war can ever come to being necessary if the world was to be spared an evil as radical as war itself. And I wouldn't have missed my part of it for anything.